Ton of refrigeration
A capacity unit equal to 12,000 BTU per hour, roughly 3.5 kilowatts. It comes from the cooling once provided by melting a ton of ice in a day, and is still standard shorthand for equipment size in North America.
Also called ton, tonnage
What is a ton of refrigeration?
A ton of refrigeration is 12,000 BTU per hour, about 3.5 kilowatts. The name comes from the cooling once produced by melting one ton of ice over twenty-four hours.
Ton of refrigeration: how it works
Before mechanical refrigeration, cooling was sold as ice, so the capacity of early machines was described by how much ice they replaced. Melting one ton of ice over twenty-four hours absorbs about 288,000 BTU, which is 12,000 BTU per hour, and the unit stuck long after the ice trade ended.
Where you meet the term
- In a quotation for central equipment, where systems are described as three ton or four ton rather than by BTU.
- In a model number, where a two-digit code can encode nominal tonnage in twelfths.
- In a sizing conversation, where a technician will quote tonnage and a European supplier will quote kilowatts.
How to check it
- Divide the BTU rating by twelve thousand. A 36,000 BTU/h system is three tons. The rating comes from the data plate rather than from the size of the cabinet. Owner check
- Confirm nominal against rated capacity. Nominal tonnage is a size class. Actual rated capacity at test conditions can differ from the round number the class implies. Technician
Figures you will see
| Condition | Figure | What it tells you |
|---|---|---|
| One ton | 12,000 BTU/h | Approximately 3.517 kW |
| Origin figure | 288,000 BTU per day | The heat absorbed melting one short ton of ice over twenty-four hours |
Ton of refrigeration: what it is not
- A ton here has nothing to do with the weight of the equipment. It is a rate of heat removal.
- Nominal tonnage is a class rather than a measured output. Two three-ton systems can have slightly different rated capacities.
Ton of refrigeration questions
How many tons is my air conditioner?
Divide the rated capacity in BTU per hour by 12,000. Many North American model numbers also encode it, as a two-digit number that is the tonnage multiplied by twelve.
Is tonnage used outside North America?
Residential equipment in the United Kingdom and Europe is quoted in kilowatts, so a three ton system appears as roughly 10.5 kW.
Does more tonnage mean better cooling?
Only if the building needs it. Oversized fixed-speed equipment satisfies the control quickly, removes less moisture, and cycles more, which is why sizing comes from a calculation.
Where this definition comes from
Written from standards body publication material held in the HVAC Bench evidence record. Where a document limits a definition to certain models, that limit is repeated here rather than generalised across a brand.
- ASHRAE TerminologyIndustry reference definitions for heating, ventilation, air conditioning, and refrigeration vocabulary.